Measuring and testing – Speed – velocity – or acceleration – Acceleration determination utilizing inertial element
Patent
1989-10-13
1991-01-15
Snow, Walter E.
Measuring and testing
Speed, velocity, or acceleration
Acceleration determination utilizing inertial element
280735, 340669, 180282, G01P 1508, B60R 2100, B60R 2132, G08B 2100
Patent
active
049844644
DESCRIPTION:
BRIEF SUMMARY
When a body is subject to excessive acceleration, such as a road vehicle in a crash, it is often desired to operate certain equipment automatically. Most acceleration responsive devices Specification No. 119064, in which a conductive sphere which is normally retained in position by a magnet is caused by the excessive acceleration to move to a position in which it bridges two contacts, completing a circuit to operate the desired equipment. An analogue electrical equivalent of the inertia sensor has been proposed, in which an electrical signal proportional to the acceleration sensed is generated and integrated in order to provide an output signal from the integrator representing the velocity change during the integration period. When this velocity signal exceeds a predetermined threshold, the desired equipment is actuated.
Although such electronic equipment is an improvement on the mechanical inertia sensors, it is subject to error since each of the components in the electronic circuit has certain tolerances, all of which can contribute to the error in the final signal, which is therefore not reliable. Analogue equipment is also susceptible to interference from radio frequencies and electromagnetic disturbances.
The present invention proposes to improve acceleration responsive devices which comprise an electronic accelerometer adapted to provide an analogue electrical signal output representative of acceleration detected together with an integrator and an operating circuit enabled by the integrator output above a predetermined level, the improvement comprising an analogue/digital converter ro provide a digital signal in response to the accelerometer output representative to the acceleration detected, the integrator being arranged to integrate the digital signal. Much better accuracy is available with digital equipment and the setting of thresholds is made much easier.
An optional feature of the invention includes an accelerometer which provides two voltage outputs, one representing the acceleration detected and the other representing zero acceleration, thus enabling any errors due to temperature changes or aging of components to be eliminated. Preferably the two outputs from the accelerometer are individually converted to digital signals and then subtracted one from the other to provide an input to the integrator.
The invention may be applied to actuation of vehicle safety equipment in a crash, such as the inflation of an air bag to form a cushion between the driver's chest and the steering wheel. In order that the air bag is not inflated by false alarms, the invention preferably includes a threshold detector responsive only to signals representing detected accelerations over a given level (so as in the vehicle safety application to ignore accelerations experienced during normal driving) and also a delay circuit to prevent actuation of the operating circuit until an acceleration over the predetermined level has been experienced from a given time (so as in the vehicle safety application to exclude short-term high accelerations caused for example by hitting a kerb or a pot-hole or by hammering during servicing of the vehicle).
The drawing shows a block diagram of the acceleration responsive circuit of the present invention.
An electronic accelerometer 11 provides two outputs, Vsig being a voltage representing the detected acceleration and Vref comprising a voltage representing a zero reference level. The accelerometer 11 is provided with both a generator of a reference voltage and an acceleration detector which generates the signal voltage.
The Vsig and Vref signals are passed to an analog/digital converter 12 where the two signals are subtracted at a sampling rate which depends upon the control signal from line 30 and the difference between the voltages is converted to a pulse train with a pulse repetition frequency which is dependent upon the signal on line 31. Line 18 provides a signal indicating whether the acceleration is positive or negative. The integrator integrates the signal from line 17, also under
REFERENCES:
patent: 3459053 (1969-08-01), Grimme et al.
patent: 4410875 (1973-10-01), Spies et al.
Kalami Hoshmand
Thomas Alan D.
First Inertia Switch Limited
Snow Walter E.
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